1. Field of the Invention
This invention relates to a method for producing large amounts of redox shuttle and more specifically, this invention relates to a method for producing at least one kilogram (kg) per batch of a redox shuttle having a first oxidation potential of approximately 4 volts (V).
2. Background of the Invention
Lithium-ion battery advances are the de facto power sources for portable electronic devices and vehicle propulsion. Rechargeable lithium-ion batteries are used for thousands of cycles with no gaseous exhaust, delivering high density energy and providing reliable and clean chemical energy storage. Compared to fossil fuels and biomass, lithium-ion batteries compare favorably in reducing air pollution and therefore global warming.
As lithium battery chemistry increases in voltage potential, so too does the need to prevent overcharging. One means for preventing overcharging is the use of electronic monitoring devices attached to each cell to monitor voltages.
Another means is the use of anti-overcharge additives to electrolyte. These additives include redox shuttle molecules. Generally, redox shuttle molecules can be reversibly oxidized and reduced at a defined potential slightly higher than the end-of-charge potential of the cathode. This mechanism can protect the cell from overcharge by locking the potential of the cathode at the oxidation potential of the shuttle molecules. Redox shuttles have been implemented for overcharge protection of 3 volts (V) class lithium-ion batteries.
Efforts have been made to provide redox shuttles with overcharge protections in excess of 4 V. See, for example U.S. Patent App. No. US 20011/0294003 A1, published Dec. 1, 2011, and incorporated herein by reference.
However, such state of the art shuttle production protocols result in extremely small yields (e.g., less than 10 grams). Also, those methods require inert environments and expensive, hazardous reagents.
Specifically, 1,4-di-tert-butyl-2,5-bis(2-methoxyethoxy)benzene has been previously used by the inventors as an effective redox shuttle. The bench chemistry of the production of the shuttle is depicted in Equation 1 below. The process for its production suffers from salient drawbacks, including the following:                It requires a 17 hour reaction time;        Only a 60 percent yield is realized;        Hazardous feed materials are used, such as sodium hydride and peroxide-forming tetrahydrofuran;        Inert, dry atmospheres are required inasmuch as anhydrous solvent is utilized;        Hydrogen is generated as a side product and needs to be vented causing explosion hazard;        The process produces a complex mixture requiring large volumes of solvents to separate the product. (For example, dichloromethane is used in the extraction, which is a highly toxic and persistent pollutant);        Purification is via chromatography, which is lengthy and requires large amounts of solvents; and        Initial batch size is less than 0.1 grams, which makes the process unsuitable for industrial scale-up.        

A need exists in the art for a method for producing redox shuttles for use in batteries that yields multiples of 500 gram quantities per processing cycle. The method should not require elaborate processing parameters nor should the method require expensive and dangerous reagents. Also, the processing cycles should last no more than 6 to 8 hours.